This type of tilt spectra along a slit was first observed for prominences ([1]}) and interpreted as rotating prominences before eruption. Thanks to the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph onboard SOHO, and now also with the IRIS spectrograph, such a tilt behaviour in the spectra is frequently observed. They are well-known and typically associated
with twist ([2]}) or rotation ([3]}),
or flows of plasma in helical
structures ([4]}). In [4]}, the
long filament crossed by the IRIS slits changed the direction of its rotation in the middle of the filament. In our observations, the jet is rotating in the same direction in all four positions. The slit scanned only 6 arc sec of the jet, mainly capturing the jet base with the dome shape. The tilt in our spectra finally reach a length around 60 pixels, which represents around 15 Mm. We interpret this tilt by the rotation of a structure crossed by the slit, the structure being the base of the jet or, possibly, cool plasma that follows helical structures.
The profiles of the Mg II k line with extended wings resemble the profiles of the IRIS bombs (IBs) that were discovered by [6]} and analysed by [7]} and [8]}. [7]} found that the IBs were formed in the very low atmosphere between 50 to 900 km in the chromosphere. The magnetic configuration of the reconnection site is similar to that of the Ellerman bombs (EBs) in BP regions, where there is no vertical magnetic field ([10]}; [8]}). We conjecture that between the two EMFs in the QSL region, there is a BP reconnection region as in IBs ([8]}). The BP topology in the region of the present jet is confirmed in the topological analysis.
The cool material which is expelled towards the east could correspond to the dark blobs that previously existed in this area, which were trapped in the BP region while the BP was forming between two mini-flare events.
